In silver-halide photography, there is a category of prepackaged photographic units, commonly called “film with lens” or “One-Time-Use Cameras” (OTUC's), wherein the consumer purchases a film element contained in a shell that incorporates a lens and shutter to sequentially expose frames of the film element. These OTUC's are purchased as a unit, used by the consumer, and returned by the consumer to a photofinishing laboratory for processing.
During manufacture of these units, the manufacturer preloads the film element in a cassette (also referred to as a cartridge or magazine), placing the tongue of the unexposed film element around a so-called supply-side spool in the dark and then pulling the film element from the cassette onto the spool leaving the end of the film attached to the spool in the cassette. In some OTUC's, the supply side spool is then removed, leaving the film tightly wound in the supply-side chamber. As the consumer exposes the film, the film is wound back into the cassette usually until all the frames are exposed. By constructing an OTUC in this fashion, the unit needs to have only one directional transport features and the cost is reduced.
Unlike conventional reloadable cameras used by consumers, the film element in a typical OTUC can spend several months with the tongue-end wound tightly into a roll, either onto the supply side spool or into a core-less spool of film. During this time, the tongue end of the film takes on core set, where the film acquires a tendency to stay coiled tightly, even when removed from the camera. The effect of core-set is particularly a problem with preloaded film in OTUC's because when preloaded the tongue of the film is held in a tighter diameter coil than in the original cartridge. This is especially true when the OTUC film element is a conventional 35 mm film comprising a cellulose tri acetate (CTA) film base. It is also especially a problem with increasingly smaller limited-size or narrow-bodied OTUC's or OTUC designs having relatively smaller diameter space for spooled or spool-less film. The high core-set curl makes it difficult for photofinishers to remove the tongue from the cassette to prepare the film for photo processing.
When a photographic film is wound on a spool it is likely to take up some core-set curl, the extent of which depends primarily on the diameter of the spool, the duration of winding (storage time) and the storage temperature. Because of the tendency to lower the size of film cartridges, hence decrease spool diameter, the problem of maintaining low core-set curl has become more acute.
The core-set propensity of the film is often measured under extreme conditions to simulate long storage times and adverse environmental conditions—the Accelerated Core-Set Test. Such tests are conducted by winding the film tightly around an actual spool and incubating the film at high temperature for a prescribed time, usually 1 day. The core-set realized in short-time, high-temperature tests simulates the core-set typically realized during actual use at room temperature and longer times. The wound film is then removed from the oven, allowed to equilibrate for some time at ambient conditions and its curl is measured according to Test Method A in American National Standard Institute (ANSI), P41.29-1985. The post-process curl (PPC) is evaluated by processing the film immediately after it is unwound from the spool in a standard minilab processor and measuring the residual curl of the processed film some prescribed time after the film exits the processor. Here too the curl is measured according to Test Method A in American National Standard Institute (ANSI), P41.29-1985.
Over the years many approaches have been taken to reduce core-set curl and/or post-process curl in photographic films. For example, U.S. Pat. No. 4,827,298 to Sasaki et al. provides film supports with superior anti-curl properties. Most approaches are associated with the film base, which normally makes the most significant contribution to the core-set curl produced by the film. These approaches can be generally divided into seven categories: (1) high-temperature annealing, (2) inherent curl, (3) ironing, (4) reverse winding, (5) addition of a restraining layer, (6) emulsion reformulation and (7) addition of moisture absorbing layers in a polyester laminate. Of these approaches, high temperature annealing is especially effective when dealing with relatively thick non-hydrophilic polyester film supports. General efforts in this regard have led to various base annealing procedures as described in U.S. Pat. Nos. 4,141,735; 5,254,445; 5,629,141 and 5,585,229. This material and other similar materials require relatively long annealing times to achieve sufficient reduction in core-set curl.
It would be desirable to utilize a film base with low core-set tendency in OTUC units. One such low core set tendency film exists in the Advanced Photo System format, poly(ethylene napthalate) or PEN. Such polyester film-base materials are well known in the trade. Both poly(ethylene napthalate) (“PEN”), and poly(ethylene terephthalate) base (PET) have been used as a film base. PEN film base has also been annealed (APEN) using a general procedure described in U.S. Pat. No. 4,141,735. Annealing temperatures used are generally in the range of from 50° C. to the glass transition temperature of the base material and for times ranging from 0.25-1000 hr.
APEN is very costly and very difficult to cut by photo-processing machines and other equipment used in a photo-processing laboratory for conventional 35 mm films comprising a CTA base. One attribute that expresses the difficulty to cut the base is the Cutting Index, defined below. Films with high Cutting Index values are harder to cut than those with Cutting Index values close to 1.0 (=value for CTA base).
U.S. Pat. No. 6,558,884 discloses a poly(ethylene terephthalate)-based photographic film base having improved properties with regard to cutting, perforating, and other finishing or photofinishing operations. The film base is made of a poly(ethylene terephthalate)-based material comprising a specified amount of monomeric units derived from 1,4-cyclohexanedimethanol, such that the film base has a specified cutting-related property.